Energy - Real-life applications

Photo by: DWP

Falling and Bouncing Balls

One of the best—and most frequently used—illustrations
of potential and kinetic energy involves standing at the top of a
building, holding a baseball over the side. Naturally, this is not an
experiment to perform in real life. Due to its relatively small mass,
a falling baseball does not have a great amount of kinetic energy, yet
in the real world, a variety of other conditions (among them inertia,
the tendency of an object to maintain its state of motion) conspire to
make a hit on the head with a baseball potentially quite serious. If
dropped from a great enough height, it could be fatal.

When one holds the baseball over the side of the building, potential
energy is at a peak, but once the ball is released, potential energy
begins to decrease in favor of kinetic energy. The relationship
between these, in fact, is inverse: as the value of one decreases,
that of the other increases in exact proportion. The ball will only
fall to the point where its potential energy becomes 0, the same
amount of kinetic energy it possessed before it was dropped. At the
same point, kinetic energy will have reached maximum value, and will
be equal to the potential energy the ball possessed at the beginning.
Thus the sum of kinetic energy and potential energy remains constant,
reflecting the conservation of energy, a subject discussed below.

It is relatively easy to understand how the ball acquires kinetic
energy in its fall, but potential energy is somewhat more challenging
to comprehend. The ball does not really "possess" the
potential energy: potential energy resides within an entire system
comprised by the ball, the space through which it falls, and the
Earth. There is thus no "magic" in the reciprocal
relationship between potential and kinetic energy: both are part of a
single system, which can be envisioned by means of an analogy.

Imagine that one has a 20-dollar bill, then buys a pack of gum. Now
one has, say, $19.20. The positive value of dollars has decreased by
$0.80, but now one has increased "non-dollars" or
"anti-dollars" by the same amount. After buying lunch,
one might be down to $12.00, meaning that "anti-dollars"
are now up to $8.00. The same will continue until the entire $20.00
has been spent. Obviously, there is nothing magical about this: the
20-dollar bill was a closed system, just like the one that included
the ball and the ground. And just as potential energy decreased while
kinetic energy increased, so "non-dollars" increased
while dollars decreased.

BOUNCING BACK.

The example of the baseball illustrates one of the most fundamental
laws in the universe, the conservation of energy: within a system
isolated from all other outside factors, the total amount of energy
remains the same, though transformations of energy from one form to
another take place. An interesting example of this comes from the case
of another ball and another form of vertical motion.

This time instead of a baseball, the ball should be one that bounces:
any ball will do, from a basketball to a tennis ball to a superball.
And rather than falling from a great height, this one is dropped
through a range of motion ordinary for a human being bouncing a ball.
It hits the floor and bounces back—during which time it
experiences a complex energy transfer.

As was the case with the baseball dropped from the building, the ball
(or more specifically, the system involving the ball and the floor)
possesses maximum potential energy prior to being released. Then, in
the split-second before its impact on the floor, kinetic energy will
be at a maximum while potential energy reaches zero.

So far, this is no different than the baseball scenario discussed
earlier. But note what happens when the ball actually hits the floor:
it stops for an infinitesimal fraction of a moment. What has happened
is that the impact on the floor (which in this example is assumed to
be perfectly rigid) has dented the surface of the ball, and this saps
the ball's kinetic energy just at the moment when the energy
had reached its maximum value. In accordance with the energy
conservation law, that energy did not simply disappear: rather, it was
transferred to the floor.

Meanwhile, in the wake of its huge energy loss, the ball is
motionless. An instant later, however, it reabsorbs kinetic energy
from the floor, undents, and rebounds. As it flies upward, its kinetic
energy begins to diminish, but potential energy increases with height.
Assuming that the person who released it catches it at exactly the
same height at which he or she let it go, then potential energy is at
the level it was before the ball was dropped.

WHEN A BALL LOSES ITS BOUNCE.

The above, of course, takes little account of energy
"loss"—that is, the transfer of energy from one
body to another. In fact, a part of the ball's kinetic energy
will be lost to the floor because friction with the floor will lead to
an energy transfer in the form of thermal, or heat, energy. The sound
that the ball makes when it bounces also requires a slight energy
loss; but friction—a force that resists motion when the surface
of one object comes into contact with the surface of another—is
the principal culprit where energy transfer is concerned.

Of particular importance is the way the ball responds in that instant
when it hits bottom and stops. Hard rubber balls are better suited for
this purpose than soft ones, because the harder the rubber, the
greater the tendency of the molecules to experience only elastic
deformation. What this means is that the spacing between molecules
changes, yet their overall position does not.

If, however, the molecules change positions, this causes them to slide
against one another, which produces friction and reduces the energy
that goes into the bounce. Once the internal friction reaches a
certain threshold, the ball is "dead"—that is,
unable to bounce. The deader the ball is, the more its kinetic energy
turns into heat upon impact with the floor, and the less energy
remains for bouncing upward.

Varieties of Energy in Action

The preceding illustration makes several references to the conversion
of kinetic energy to thermal energy, but it should be stressed that
there are only three fundamental varieties of energy: potential,
kinetic, and rest. Though heat is often discussed as a form unto
itself, this is done only because the topic of heat or thermal energy
is complex: in fact, thermal energy is simply a result of the kinetic
energy between molecules.

To draw a parallel, most languages permit the use of only three basic
subject-predicate constructions: first person ("I"),
second person ("you"), and third person
("he/she/it.") Yet within these are endless varieties
such as singular and plural nouns or various temporal orientations of
verbs: present ("I go"); present perfect ("I have
gone"); simple past ("I went"); past perfect
("I had gone.") There are even "moods,"
such as the subjunctive or hypothetical, which permit the construction
of complex thoughts such as "I would have gone." Yet for
all this variety in terms of sentence pattern—actually, a
degree of variety much greater than for that of energy
types—all subject-predicate constructions can still be
identified as first, second, or third person.

One might thus describe thermal energy as a manifestation of energy,
rather than as a discrete form. Other such manifestations include
electromagnetic (sometimes divided into electrical and magnetic),
sound, chemical, and nuclear. The principles governing most of these
are similar: for instance, the positive or negative attraction between
two electromagnetically charged particles is analogous to the force of
gravity.

MECHANICAL ENERGY.

One term not listed among manifestations of energy is mechanical
energy, which is something different altogether: the sum of potential
and kinetic energy. A dropped or bouncing ball was used as a
convenient illustration of interactions within a larger system of
mechanical energy, but the example could just as easily have been a
roller coaster, which, with its ups and downs, quite neatly
illustrates the sliding scale of kinetic and potential energy.

Likewise, the relationship of Earth to the Sun is one of potential and
kinetic energy transfers: as with the baseball and Earth itself, the
planet is pulled by gravitational force toward the larger body. When
it is relatively far from the Sun, it possesses a higher degree of
potential energy, whereas when closer, its kinetic energy is highest.
Potential and kinetic energy can also be illustrated within the realm
of electromagnetic, as opposed to gravitational, force: when a nail is
some distance from a magnet, its potential energy is high, but as it
moves toward the magnet, kinetic energy increases.

ENERGY CONVERSION IN A DAM.

A dam provides a beautiful illustration of energy conversion: not only
from potential to kinetic, but from energy in which gravity provides
the force component to energy based in electromagnetic force. A dam
big enough to be used for generating hydroelectric power forms a vast
steel-and-concrete curtain that holds back millions of tons of water
from a river or other body. The water nearest the top—the
"head" of the dam—thus has enormous potential
energy.

Hydroelectric power is created by allowing controlled streams of this
water to flow downward, gathering kinetic energy that is then
transferred to powering turbines. Dams in popular vacation spots often
release a certain amount of water for recreational purposes during the
day. This makes it possible for rafters, kayakers, and others
downstream to enjoy a relatively fast-flowing river. (Or, to put it
another way, a stream with high kinetic energy.) As the day goes on,
however, the sluice-gates are closed once again to build up the
"head." Thus when night comes, and energy demand is
relatively high as people retreat to their homes, vacation cabins, and
hotels, the dam is ready to provide the power they need.

OTHER MANIFESTATIONS OF ENERGY.

Thermal and electromagnetic energy are much more readily recognizable
manifestations of energy, yet sound and chemical energy are two forms
that play a significant part as well. Sound, which is essentially
nothing more than the series of pressure fluctuations within a medium
such as air, possesses enormous energy: consider the example of a
singer hitting a certain note and shattering a glass.

Contrary to popular belief, the note does not have to be particularly
high: rather, the note should be on the same wavelength as the
glass's own vibrations. When this occurs, sound energy is
transferred directly to the glass, which is shattered by this sudden
net intake of energy. Sound waves can be much more destructive than
that: not only can the sound of very loud music cause permanent damage
to the ear drums, but also, sound waves of certain frequencies and
decibel levels can actually drill through steel. Indeed, sound is not
just a by-product of an explosion; it is part of the destructive
force.

As for chemical energy, it is associated with the pull that binds
together atoms within larger molecular structures. The formation of
water molecules, for instance, depends on the chemical bond between
hydrogen and oxygen atoms. The combustion of materials is another
example of chemical energy in action.

With both chemical and sound energy, however, it is easy to show how
these simply reflect the larger structure of potential and kinetic
energy discussed earlier. Hence sound, for instance, is potential
energy when it emerges from a source, and becomes kinetic energy as it
moves toward a receiver (for example, a human ear). Furthermore, the
molecules in a combustible material contain enormous chemical
potential energy, which becomes kinetic energy when released in a
fire.

Rest Energy and Its Nuclear Manifestation

Nuclear energy is similar to chemical energy, though in this instance,
it is based on the binding of particles within an atom and its
nucleus. But it is also different from all other kinds of energy,
because its force component is neither gravitational nor
electromagnetic, but based on one of two other known varieties of
force: strong nuclear and weak nuclear. Furthermore, nuclear
energy—to a much greater extent than thermal or chemical
energy—involves not only kinetic and potential energy, but also
the mysterious, extraordinarily powerful, form known as rest energy.

Throughout this discussion, there has been little mention of rest
energy; yet it is ever-present. Kinetic and potential energy rise and
fall with respect to one another; but rest energy changes little. In
the baseball illustration, for instance, the ball had the same rest
energy at the top of the building as it did in flight—the same
rest energy, in fact, that it had when sitting on the ground. And its
rest energy is enormous.

NUCLEAR WARFARE.

This brings back the subject of the rest energy formula:
E
=
mc
2
, famous because it made possible the creation of the atomic bomb. The
latter, which fortunately has been detonated in warfare only twice in
history, brought a swift end to World War II when the United States
unleashed it against Japan in August 1945. From the beginning, it was
clear that the atom bomb possessed staggering power, and that it would
forever change the way nations conducted their affairs in war and
peace.

Yet the atom bomb involved only nuclear fission, or the splitting of
an atom, whereas the hydrogen bomb that appeared just a few years
after the end of World War II used an even more powerful process, the
nuclear fusion of atoms. Hence, the hydrogen bomb upped the ante to a
much greater extent, and soon the two nuclear superpowers—the
United States and the Soviet Union—possessed the power to
destroy most of the life on Earth.

The next four decades were marked by a superpower struggle to control
"the bomb" as it came to be known—meaning any and
all nuclear weapons. Initially, the United States controlled all
atomic secrets through its heavily guarded Manhattan Project, which
created the bombs used against Japan. Soon, however, spies such as
Julius and Ethel Rosenberg provided the Soviets with U.S. nuclear
secrets, ensuring that the dictatorship of Josef Stalin would possess
nuclear capabilities as well. (The Rosenbergs were executed for
treason, and their alleged innocence became a celebrated cause among
artists and intellectuals; however, Soviet documents released since
the collapse of the Soviet empire make it clear that they were guilty
as charged.)

Both nations began building up missile arsenals. It was not, however,
just a matter of the United States and the Soviet Union. By the 1970s,
there were at least three other nations in the "nuclear
club": Britain, France, and China. There were also other
countries on the verge of developing nuclear bombs, among them India
and Israel. Furthermore, there was a great threat that a terrorist
leader such as Libya's Muammar al-Qaddafi would acquire nuclear
weapons and do the unthinkable: actually use them.

Though other nations acquired nuclear weapons, however, the scale of
the two super-power arsenals dwarfed all others. And at the heart of
the U.S.-Soviet nuclear competition was a sort of high-stakes chess
game—to use a metaphor mentioned frequently during the 1970s.
Soviet leaders and their American counterparts both recognized that it
would be the end of the world if either unleashed their nuclear
weapons; yet each was determined to be able to meet the other's
ever-escalating nuclear threat.

United States President Ronald Reagan earned harsh criticism at home
for his nuclear buildup and his hard line in negotiations with Soviet
President Mikhail Gorbachev; but as a result of this one-upmanship, he
put the Soviets into a position where they could no longer compete. As
they put more and more money into nuclear weapons, they found
themselves less and less able to uphold their already weak economic
system. This was precisely Reagan's purpose in using American
economic might to outspend the Soviets—or, in the case of the
proposed multi-trillion-dollar Strategic Defense Initiative (SDI or
"Star Wars")—threatening to outspend them. The
Soviets expended much of their economic energy in competing with U.S.
military strength, and this (along with a number of other complex
factors), spelled the beginning of the end of the Communist empire.

E = MC
2
.

The purpose of the preceding historical brief is to illustrate the
epoch-making significance of a single scientific formula:
E
=
mc
2
. It ended World War II and ensured that no war like it would ever
happen again—but brought on the specter of global annihilation.
It created a superpower struggle—yet it also ultimately helped
bring about the end of Soviet totalitarianism, thus opening the way
for a greater level of peace and economic and cultural exchange than
the world has ever known. Yet nuclear arsenals still remain, and the
nuclear threat is far from over.

So just what is this literally earth-shattering formula?
E
stands for rest energy,
m
for mass, and
c
for the speed of light, which is 186,000 mi (297,600 km) per second.
Squared, this yields an almost unbelievably staggering number.

Hence, even an object of insignificant mass possesses an incredible
amount of rest energy. The baseball, for instance, weighs only about
0.333 lb, which—on Earth, at least—converts to 0.15 kg.
(The latter is a unit of mass, as opposed to weight.) Yet when
factored into the rest energy equation, it yields about 3.75 billion
kilowatt-hours—enough to provide an American home with enough
electrical power to last it more than 156,000 years!

How can a mere baseball possess such energy? It is not the baseball in
and of itself, but its mass; thus every object with mass of any kind
possesses rest energy. Often, mass energy can be released in very
small quantities through purely thermal or chemical processes: hence,
when a fire burns, an almost infinitesimal portion of the matter that
went into making the fire is converted into energy. If a stick of
dynamite that weighed 2.2 lb (1 kg) exploded, the portion of it that
"disappeared" would be equal to 6 parts out of 100
billion; yet that portion would cause a blast of considerable
proportions.

As noted much earlier, the derivation of Einstein's
formula—and, more to the point, how he came to recognize the
fundamental principles involved—is far beyond the scope of this
essay. What is important is the fact, hypothesized by Einstein and
confirmed in subsequent experiments, that matter is convertible to
energy, a fact that becomes apparent when matter is accelerated to
speeds close to that of light.

Physicists do not possess a means for propelling a baseball to a speed
near that of light—or of controlling its behavior and capturing
its energy. Instead, atomic energy—whether of the wartime or
peacetime varieties (that is, in power plants)—involves the
acceleration of mere atomic particles. Nor is any atom as good as
another. Typically physicists use uranium and other extremely rare
minerals, and often, they further process these minerals in highly
specialized ways. It is the rarity and expense of those minerals,
incidentally—not the difficulty of actually putting atomic
principles to work—that has kept smaller nations from
developing their own nuclear arsenals.